System for recovering waste heat

ABSTRACT

A waste heat recovery system includes a heat generation system including at least two separate heat sources having different temperatures. A rankine cycle system is coupled to the at least two separate heat sources and configured to circulate a working fluid. The rankine cycle system is coupled to at least one heat source and another heat source among the at least two separate heat sources. The rankine cycle system is configured to remove heat from the at least one heat source to partially vaporize or preheat the working fluid; and remove heat from the other heat source to vaporize or superheat the working fluid.

BACKGROUND

The embodiments disclosed herein relate generally to the field of power generation and, more particularly, to a system for recovering waste heat from a plurality of heat sources having different temperatures for generation of electricity.

Enormous amounts of waste heat are generated by a wide variety of industrial and commercial processes and operations. Example sources of waste heat include heat from space heating assemblies, steam boilers, engines, and cooling systems. When waste heat is low grade, such as waste heat having a temperature of heat below 400 degrees Fahrenheit, for example, conventional heat recovery systems do not operate with sufficient efficiency to make recovery of energy cost-effective. The net result is that vast quantities of waste heat are simply dumped into the surroundings.

Combustion engines are also used to generate electricity using fuels such as gasoline, natural gas, biogas, plant oil, and diesel fuel. However, atmospheric emissions such as nitrogen oxides and particulates may be emitted.

In one conventional method to generate electricity from waste heat, a two-cycle system is used in heat recovery applications with waste heat sources of different temperature levels. In such two-cycle configurations, the hot heat source heats a high-boiling point liquid in a top loop, and the cold heat source heats a low-boiling point liquid in a separate bottom loop. Since the two-cycle systems are more complex and require more components, the overall cost of the two-cycle system is significantly higher.

In another conventional system provided to generate electricity from waste heat, a cascaded organic rankine cycle system for utilization of waste heat includes a pair of organic rankine cycle systems. The cycles are combined, and the respective organic working fluids are chosen such that the organic working fluid of the first organic rankine cycle is condensed at a condensation temperature that is above the boiling point of the organic working fluid of the second organic cycle. A single common heat exchanger is used for both the condenser of the first organic rankine cycle system and the evaporator of the second organic rankine cycle. A cascaded organic rankine cycle system converts surplus heat into electricity within certain temperature ranges but does not recover waste heat over a wide temperature range. Another disadvantage is the requirement of two separate expander/generator units in each cycle, which increases complexity of the overall system.

It would be desirable to have a system that effectively recovers waste heat over a wide temperature range from multiple low-grade heat sources.

BRIEF DESCRIPTION

In accordance with one exemplary embodiment of the present invention, a waste heat recovery system is disclosed. The waste heat recovery system includes a heat generation system including at least two separate heat sources having different temperatures. A rankine cycle system is coupled to the at least two separate heat sources and configured to circulate a working fluid. The rankine cycle system is coupled to at least one heat source and another heat source among the at least two separate heat sources. The rankine cycle system is configured to remove heat from the at least one heat source to partially vaporize or preheat the working fluid and remove heat from the other heat source to vaporize or superheat the working fluid.

In accordance with another exemplary embodiment of the present invention, a waste heat recovery system is disclosed. The waste heat recovery system includes a heat generation system including at least two separate heat sources having different temperatures. A rankine cycle system is coupled to the at least two separate heat sources and configured to circulate a working fluid. The rankine cycle system includes a condenser coupled to at least one heat source among the at least two separate heat sources. Heat from the at least one heat source is used to partially vaporize or preheat the working fluid. An evaporator is coupled to another heat source among the at least two separate heat sources and configured to remove heat from the other heat source to vaporize or superheat the working fluid.

In accordance with another exemplary embodiment of the present invention, a waste heat recovery system is disclosed. The waste heat recovery system includes a heat generation system including at least two separate heat sources having different temperatures. A rankine cycle system is coupled to the at least two separate heat sources and configured to circulate a working fluid. The rankine cycle system includes an evaporator coupled to at least one heat source and another heat source among the at least two separate heat sources. The heat from the at least one heat source and the other heat source is used to heat water. The heated water is circulated in heat exchange relationship with the working fluid via the evaporator to vaporize the working fluid.

In accordance with another exemplary embodiment of the present invention, a waste heat recovery system is disclosed. The waste heat recovery system includes a heat generation system including at least two separate heat sources having different temperatures. A rankine cycle system is coupled to the at least two separate heat sources and configured to circulate a working fluid. The rankine cycle system includes a condenser coupled to at least one heat source among the at least two separate heat sources. The working fluid is circulated through the at least one heat source to remove heat from the at least one heat source to partially vaporize or preheat the working fluid from the condenser. An evaporator is coupled to another heat source among the at least two separate heat sources. The working fluid is circulated through the evaporator to remove heat from the other heat source to completely vaporize or superheat the working fluid.

DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagrammatical representation of a waste heat recovery system having a heat generation system and a rankine cycle systems in accordance with an exemplary embodiment disclosed herein;

FIG. 2 is a diagrammatical representation of a waste heat recovery system having a heat generation system and a rankine cycle systems in accordance with an exemplary embodiment disclosed herein;

FIG. 3 is a diagrammatical representation of a waste heat recovery system having a heat generation system and a rankine cycle systems in accordance with an exemplary embodiment disclosed herein; and

FIG. 4 is a diagrammatical representation of a waste heat recovery system having a heat generation system and a rankine cycle systems in accordance with an exemplary embodiment disclosed herein.

DETAILED DESCRIPTION

As discussed in detail below, embodiments of the present invention provide a waste heat recovery system having a heat generation system and one rankine cycle system. The heat generation system includes at least two separate heat sources having different temperatures. The rankine cycle system is coupled to at least two separate heat sources and configured to circulate a working fluid. The rankine cycle system is coupled to at least one heat source among the at least two separate heat sources and configured to remove heat from the at least one heat source to partially vaporize or preheat the working fluid before completely vaporizing or superheating the working fluid. The rankine cycle system is also coupled to another heat source among the at least two separate heat sources and configured to remove heat from the other heat source to completely vaporize or superheat the working fluid. In accordance with the exemplary embodiments of the present invention, the waste heat recovery system is integrated with multiple low-grade heat sources to allow a higher efficient recovery of waste heat for generation of electricity. In certain embodiments, the working fluid is used directly for cooling the heat generation system. Although the waste heat recovery system in the exemplary embodiments of FIGS. 1-4 is described with reference to combustion engines, the system is also applicable to other heat generation systems such as gas turbines, geothermal, solar thermal, industrial and residential heat sources, or the like.

Referring to FIG. 1, a waste heat recovery system 10 is illustrated in accordance with an exemplary embodiment of the present invention. The illustrated waste heat recovery system 10 includes an rankine cycle system 12. A working fluid is circulated through the rankine cycle system 12. The working fluid may include, for example, an organic working fluid including propane, butane, pentafluoro-propane, pentafluoro-butane, pentafluoro-polyether, silicone oil, cyclohexane, cyclopentane, thiophene, ketones, aromatics, or combinations thereof. It should be noted herein that the list of organic working fluids is not exhaustive and other organic working fluids applicable to organic rankine cycles are also envisaged. In certain other embodiments, the working fluid may include water or non-organic fluids. In the illustrated embodiment, the rankine cycle system 12 includes an evaporator 14 coupled to a heat source 16 (may also be referred to as “other heat source”), for example an exhaust unit of a heat generation system 18 (for example, an engine) via a separate exhaust gas heat exchanger 20. In certain other embodiments, the heat generation system 18 may include inter-cooled gas turbines. In one example, the temperature of the exhaust unit 16 of the engine may be in the temperature range of about 300 to about 500 degrees Celsius. In the illustrated embodiment, the separate exhaust gas heat exchanger 20 is a shell and tube type heat exchanger. The exhaust gas heat exchanger 20 is used to heat thermal oil or water to a relatively higher temperature using exhaust gas of the engine. In one example, the thermal oil or water is heated from about 150 to about 300 degrees Celsius. The evaporator 14 receives heat from the heated thermal oil or water and generates a working fluid vapor. The thermal oil is then pumped back from the evaporator 14 to the exhaust gas heat exchanger 20 using a pump 22. In another embodiment, the evaporator 14 may be directly coupled to the engine exhaust unit 16.

The working fluid vapor is passed through an expander 24 to drive a generator unit 28. In certain other exemplary embodiments, the expander 24 may be a radial type expander, axial type expander, impulse type expander, or screw type expander. In certain other embodiments, the expander 24 may be coupled via a mechanical coupling to a crankshaft. In a more specific embodiment, mechanical power may be used directly for other applications. After passing through the expander 24, the working fluid vapor (at a relatively lower pressure and lower temperature) is passed through a condenser 30. The working fluid vapor is condensed into a liquid, which is then pumped using a pump 32, sequentially through one or more of a plurality of other heat sources (also referred to as “at least one heat source”) such as a low-temperature intercooler 34, an oil heat exchanger 36, a cooling water jacket heat exchanger 38, and a high-temperature intercooler 40 to the evaporator 14. It should be noted herein that the other heat source includes a lower temperature heat source than the heat source 16. In one example, the temperature of the other heat source may be in the range of 80 to 100 degrees Celsius. The cycle may then be repeated. In the illustrated embodiment, a pump 42 is provided to circulate cooling water between the jacket heat exchanger 38 and an engine jacket 44. It should be noted that in other exemplary embodiments, the heat sources might include other multiple low-grade heat sources such as gas turbines with intercoolers.

In certain embodiments, the low-temperature intercooler 34 (illustrated in FIG. 1), the oil heat exchanger 36, and the cooling water jacket heat exchanger 38 are disposed upstream of the evaporator 14, and the high-temperature intercooler 40 may be disposed downstream of the evaporator 14. In such embodiments, the lower temperature intercooler 34 performs preheating of the working fluid flowing to the evaporator 14. The higher temperature intercooler 40 provided downstream of the evaporator 14 is used to heat the working fluid exiting from the evaporator 14 to a relatively higher temperature, to completely evaporate or superheat the working fluid. The provision of the lower temperature intercooler 34 and the higher temperature intercooler 40 respectively to both upstream and downstream of the evaporator 14 facilitates effective heating of the working fluid and thereby enables effective heat recovery.

In the exemplary embodiment, the working fluid is not expanded below the atmospheric pressure. The boiling point temperature of the working fluid is below the average temperature of the other heat source. The rankine cycle system 12 facilitates heat recovery from a plurality of heat sources over a temperature range. In one embodiment, the low-temperature intercooler 34, the oil heat exchanger 36, the cooling water jacket heat exchanger 38, and the high-temperature intercooler 40 are coupled along a single cooling loop and are configured to heat and partially evaporate or preheat the working fluid. In a more specific embodiment, the low-temperature intercooler may be cooled via a separate air cooler/water loop. The evaporator 14 receives the preheated or partially vaporized working fluid and is configured to vaporize or superheat the working fluid. The illustrated layout of the other heat sources 34, 36, 38, 40, and 44 facilitates effective heat removal from the plurality of lower temperature engine heat sources. This increases the effectiveness of the cooling systems and provides effective conversion of waste heat into electricity. In another exemplary embodiment of the present invention, the heat generation system may include a gas turbine system.

Referring to FIG. 2, a waste heat recovery system 10 is illustrated in accordance with an exemplary embodiment of the present invention. As discussed previously, the working fluid is circulated through the rankine cycle system 12. In the illustrated embodiment, the evaporator 14, and the condenser 30 are coupled to the plurality of other heat sources such as the oil heat exchanger 36, the engine jacket 44, and the high-temperature intercooler 40 via a partial evaporator 46. The partial evaporator 46 receives heat from a cooling water loop that collects heat from the oil heat exchanger 36, the engine jacket 44, and the high-temperature intercooler 40 and generates a partially evaporated or preheated working fluid. A pump 48 is used to circulate the water between the partial evaporator 46 and the oil heat exchanger 36, the engine jacket 44, and the high-temperature intercooler 40. The working fluid stream is passed through the evaporator 14 for evaporation or superheating of the working fluid. The vaporized working fluid vapor is passed through the expander 24 to drive the generator unit 28.

After passing through the expander 24, the working fluid vapor (at lower pressure and lower temperature) is passed through the condenser 30. The working fluid vapor is condensed into a liquid, which is then pumped via the pump 32 to the partial evaporator or preheater 46. As discussed above, the partial evaporator 46 is configured to preheat and partially evaporate the liquid being supplied to the evaporator 14.

Referring to FIG. 3, a waste heat recovery system 10 is illustrated in accordance with an exemplary embodiment of the present invention. As discussed previously, the working fluid is circulated through the rankine cycle system 12. In the illustrated embodiment, the evaporator 14 is coupled to the heat source 16, for example the exhaust unit of a heat generation system via the separate exhaust gas heat exchanger 20. The evaporator is directly coupled to the plurality of other heat sources such as the oil heat exchanger 36, the engine jacket 44, and the high-temperature intercooler 40. The evaporator 14 receives heat from a cooling water loop that collects heat from the oil heat exchanger 36, the engine jacket 44, the high-temperature intercooler 40, and the exhaust gas heat exchanger 20, and generates a vaporized or superheated working fluid. A pump 50 is used to circulate the water between the evaporator 14, the oil heat exchanger 36, the engine jacket 44, the high-temperature intercooler 40, and the exhaust gas heat exchanger 20. The vaporized working fluid vapor is passed through the expander 24 to drive the generator unit 28.

After passing through the expander 24, the working fluid vapor (at lower pressure and lower temperature) is passed through the condenser 30. The working fluid vapor is condensed into a liquid, which is then pumped via the pump 32 to the evaporator 14. As discussed above, the evaporator 14 is configured to evaporate or superheat the liquid being supplied to the evaporator 14.

Referring to FIG. 4, a waste heat recovery system 10 is illustrated in accordance with an exemplary embodiment of the present invention. The illustrated waste heat recovery system 10 includes a rankine cycle system 12. In the illustrated embodiment, the rankine cycle system 12 includes the evaporator 14 coupled to the heat source 16, for example the exhaust unit of a heat generation system (for example, an engine) via the separate exhaust gas heat exchanger 20. The exhaust gas heat exchanger 20 is used to heat thermal oil or water to a relatively higher temperature using exhaust gas of the engine. The evaporator 14 receives heat from the heated thermal oil or water and generates a working fluid vapor. The thermal oil is then pumped back from the evaporator 14 to the exhaust gas heat exchanger 20 using the pump 22.

The working fluid vapor is passed through the expander 24 to drive the generator unit 28. After passing through the expander 24, the working fluid vapor at a relatively lower pressure and lower temperature is passed through the condenser 30. The working fluid vapor is condensed into a liquid, which is then pumped using the pump 32, sequentially through a plurality of other heat sources such as the low-temperature intercooler 34, the oil heat exchanger 36, the engine jacket 44, and the high-temperature intercooler 40 to the evaporator 14. It should be noted herein that the working fluid is directly passed through the engine jacket 44 to remove heat from the engine.

In the illustrated embodiment, the low-temperature intercooler 34, the oil heat exchanger 36, the engine jacket 44, and the high-temperature intercooler 40 are coupled along a single cooling loop and are configured to heat and partially evaporate or preheat the working fluid. The evaporator 14 receives the preheated or partially vaporized working fluid and is configured to completely vaporize or superheat the working fluid. In the above discussed embodiments, the working fluid may include organic working fluid, or water, or non-organic working fluid. The illustrated layout of the other heat sources facilitates effective heat removal from the plurality of lower temperature engine heat sources. This increases the effectiveness of the cooling systems and provides effective conversion of waste heat into electricity.

As discussed above, the engine cooling system is modified such that the working fluid of the power cycle directly serves as cooling fluid for the different engine internal heat sources. In some embodiments, the working fluid flows through the existing engine heat exchangers and is preheated before being evaporated using heat from the engine exhaust gas. In certain other embodiments, the existing cooling water system is used to collect heat from the various engine heat sources and transfers heat into the waste heat cycle via intermediate heat exchangers. It should be noted herein that with reference to FIGS. 1-4 that the number of other heat sources such as intercoolers, oil heat exchangers, jacket heat exchangers evaporators and their relative positions are exemplary embodiments. The number of other heat sources and their relative positions in the rankine cycle system may be varied depending the application. All such permutations and combinations are envisaged. Also, all permutations and combinations of embodiments discussed with reference to FIGS. 1-4 are also envisaged.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. 

1. A waste heat recovery system comprising: a heat generation system comprising at least two separate heat sources having different temperatures; and a rankine cycle system coupled to the at least two separate heat sources and configured to circulate a working fluid; wherein the rankine cycle system is coupled to at least one heat source and another heat source among the at least two separate heat sources; wherein the rankine cycle system is configured to remove heat from the at least one heat source to partially vaporize or preheat the working fluid; and remove heat from the other heat source to vaporize or superheat the working fluid.
 2. The recovery system of claim 1, wherein the rankine cycle system further comprises an evaporator coupled to the other heat source, and wherein the other heat source comprises an engine exhaust unit.
 3. The recovery system of claim 2, wherein an exhaust gas from the engine exhaust unit is circulated in heat exchange relationship with the working fluid via the evaporator to completely vaporize or superheat the working fluid.
 4. The recovery system of claim 2, wherein the evaporator is coupled to the engine exhaust unit via a separate exhaust gas heat exchanger.
 5. The recovery system of claim 4, wherein an exhaust gas from the engine exhaust unit is circulated in heat exchange relationship with thermal oil or water via the separate exhaust gas heat exchanger to heat the thermal oil or water.
 6. The recovery system of claim 5, wherein the heated thermal oil or water is circulated in heat exchange relationship with the working fluid via the evaporator to completely vaporize or superheat the working fluid.
 7. The recovery system of claim 1, wherein the rankine cycle system comprises an expander coupled to the evaporator and a generator unit; wherein the expander comprises at least one radial type expander, axial type expander, screw type or impulse type expander.
 8. The recovery system of claim 1, wherein the rankine cycle system comprises a condenser, an expander, and the at least one heat source selected from a group comprising an oil heat exchanger, an engine jacket, a water jacket heat exchanger, a lower temperature intercooler, a higher temperature intercooler, or combinations thereof.
 9. The recovery system of claim 1, wherein the working fluid comprises an organic fluid comprising propane, butane, pentafluoro-propane, pentafluoro-butane, pentafluoro-polyether, silicone oil, cyclohexane, cyclopentane, thiophene, ketones, aromatics, or combinations thereof.
 10. The recovery system of claim 1, wherein the heat generation system comprises a combustion engine.
 11. A waste heat recovery system comprising: a heat generation system comprising at least two separate heat sources having different temperatures; and a rankine cycle system coupled to the at least two separate heat sources and configured to circulate a working fluid; wherein the rankine cycle system comprises: a condenser coupled to at least one heat source among the at least two separate heat sources; wherein heat from the at least one heat source is used to partially vaporize or preheat the working fluid; an evaporator coupled to another heat source among the at least two separate heat sources and configured to and remove heat from the other heat source to vaporize or superheat the working fluid. 12 The recovery system of claim 11, wherein the other heat source comprises an engine exhaust unit; wherein an exhaust gas from the engine exhaust unit is circulated in heat exchange relationship with the working fluid via the evaporator to vaporize or superheat the working fluid.
 13. The recovery system of claim 12, wherein the evaporator is coupled to the engine exhaust unit via a separate exhaust gas heat exchanger.
 14. The recovery system of claim 13, wherein an exhaust gas from the engine exhaust unit is circulated in heat exchange relationship with thermal oil or water via the separate exhaust gas heat exchanger to heat the thermal oil or water.
 15. The recovery system of claim 14, wherein the heated thermal oil or water is circulated in heat exchange relationship with the working fluid via the evaporator to completely vaporize or superheat the working fluid.
 16. The recovery system of claim 12, wherein the at least one heat source selected from a group comprising an oil heat exchanger, an engine jacket, a water jacket heat exchanger, a lower temperature intercooler, a higher temperature intercooler, or combinations thereof.
 17. The recovery system of claim 16, further comprising a partial evaporator; wherein the condenser is coupled to the oil heat exchanger, the engine jacket, the water jacket heat exchanger, the engine jacket, the lower temperature intercooler, the higher temperature intercooler, or combinations thereof through the partial evaporator configured to preheat or partially evaporate the working fluid before entering the evaporator.
 18. The recovery system of claim 17, wherein heated water is circulated in heat exchange relationship with the working fluid through the partial evaporator to preheat or partially evaporate the working fluid before entering the evaporator.
 19. A waste heat recovery system comprising: a heat generation system comprising at least two separate heat sources having different temperatures; and a rankine cycle system coupled to the at least two separate heat sources and configured to circulate a working fluid; wherein the rankine cycle system comprises: an evaporator coupled to at least one heat source and another heat source among the at least two separate heat sources; wherein heat from the at least one heat source and the other heat source is used to heat water; wherein the heated water is circulated in heat exchange relationship with the working fluid via the evaporator to vaporize the working fluid.
 20. The recovery system of claim 19; wherein the other heat source comprises an engine exhaust unit; wherein the evaporator is coupled to the engine exhaust unit via an intermediate heat exchanger.
 21. The recovery system of claim 20; wherein an exhaust gas from the engine exhaust unit is circulated in heat exchange relationship with water via the intermediate heat exchanger to heat the water.
 22. The recovery system of claim 21; wherein the at least one heat source is selected from a group comprising an oil heat exchanger, an engine jacket, a water jacket heat exchanger, a lower temperature intercooler, a higher temperature intercooler, or combinations thereof.
 23. A waste heat recovery system comprising: a heat generation system comprising at least two separate heat sources having different temperatures; and a rankine cycle system coupled to the at least two separate heat sources and configured to circulate a working fluid; wherein the rankine cycle system comprises: a condenser coupled to at least one heat source among the at least two separate heat sources; wherein working fluid is circulated through the at least one heat source to remove heat from the at least one heat source to partially vaporize or preheat the working fluid from the condenser; and an evaporator coupled to another heat source among the at least two separate heat sources; wherein the working fluid is circulated through the evaporator to remove heat from the other heat source to completely vaporize or superheat the working fluid.
 24. The recovery system of claim 23; wherein the other heat source comprises an engine exhaust unit; wherein the evaporator is coupled to the engine exhaust unit via a separate exhaust gas heat exchanger.
 25. The recovery system of claim 23; wherein the at least one heat source comprises an engine jacket; wherein working fluid is circulated through the engine jacket to remove heat from an engine and partially vaporize or preheat the working fluid from the condenser. 